Process of modifying a hydrohalogen polymer surface

ABSTRACT

This invention relates to methods of modifying a hydrohalogen polymer surface which comprises contacting a hydrohalogen polymer surface with an alkali metal alkoxide MOR wherein M is an alkali metal and R is an alkyl group thereby forming an alkoxideactivated surface and contacting said alkoxide-activated surface with an oxidizing agent thereby forming an oxygen-activated alkoxide-activated surface which is capable of accepting an electroless metal deposit.

u United States Patent [151 3,639,153

Waggoner et all, Feb, 11, 11972 [54] PRUCESS 0F MODIFYING A 3,067,078 12/1962 Gluck ..16l/l19 HYDRUHALUGEN POLYMER 3,142,581 7/1964 Leland SURFA/CE 3,167,491 1/1965 Harrison et al. 3,370,974 2/1968 Hepfer [72] lnventors: Terry Bill Waggoner, Royal Oak; Edgar 3,392,035 7/1968 Torigaiet al ..l17/l60 X John Seyb,Jr., Oak Park, both of Mich. Primary Examiner-Ralph S. Kendall [73] Asslgnee' M & T Chemicals New York Att0rneyLewis C. Brown, Kenneth G. Wheeless and Robert [22] Filed: Aug. 25, 1966 P. Grindle [21] App1.No.: 574,954 [57] ABSTRACT This invention relates to methods of modifying a [52] ILLS. Cl ..1l]l7/]11l8, 117/47 A, hydrohalogen polymer Surface which comprises contacting a um Cl (373C 3/02 hydrohalogen polymer surface with an alkali metal alltoxide [58] w 8 H8 MOR wherein M is an alkali metal and R is an alkyl group 1 R, 61, thereby forming an alkoxide-activated surface and contacting said alkoxide-activated surface with an oxidizing agent {56] References Cited thereby forming an oxygen-activated alkoxide-activated surface which is capable of accepting an electroless metal UN lTEl) STATES PATENTS p 2,943,937 7/1960 2 Claims, No Drawings Nadeau et al. ..l17/47 X PROCESS F MUDWWNG A HYDROHALOGEN POLYMER SURFACE This invention relates to the modification of plastic surfaces. More particularly, it relates to the modification of the surface of a hydrohalogen-containing polymer to render it receptive to a deposited metal plate.

it is known that various nonmetallic articles may be plated with suitable metals. It has been particularly difficuit, how ever, to obtain satisfactory plated metal surfaces on many plastics, particularly hydrohalogen polymers such as polyvinyl chloride because of the tendency of the plated metal to peel, blister, or otherwise separate from the plastic polymer substrate. Better adhesion between a chemically deposited metal plate and a plastic surface may be obtained by roughening the surface of the plastic prior to deposition of the metal. However, this method of increasing adhesion has inherent deficiencies because the chemically deposited metal plate conforms to the surface characteristics of the plastic substrate and duplicates the same surface defects. A roughened plastic surface may yield a better metal-plastic bond, but the plated surface may have an unsatisfactory dull or coarse appearance corresponding to the finish of the roughened plastic surface.

it is an object of this invention to provide a method of modifying a plastic surface of hydrohalogen polymer prior to plating the plastic material so as to render the surface more adaptable for metal plating. A further object of the invention is to provide hydrohalogen polymeric materials having a coherent metal plated surface. Other objects will be apparent to those skilled in the art from the following description.

In accordance with certain of its aspects, the process of the present invention for modifying a hydrohalogen polymer surface may comprise contacting the hydrohalogen polymer surface with an alkali metal alkoxide MOR wherein M is an alkali metal and R is an alkyl group thereby forming an alkoxide activated surface.

The hydrohalogen polymer surfaces which may be treated in practice of this invention may include those having, in the polymer, at least one group. In this group X may be a halogen atom selected from the group consisting of fluorine, chlorine, bromine, and iodine. Preferably, X may be an active halogen atom selected from the group consisting of chlorine and bromine. Preferably X may be chlorine.

The hydrohalogen polymer surfaces may preferably be chlorine-containing polymers and preferably polymers of vinyl chloride or vinylidene chloride. They may be homopolymers of polyvinyl chloride, of polyvinylidene chloride, or of polyvinyl dichloride. They may be copolymers of these compositions with other ethylenically unsaturated monomers. Ethylenically unsaturated monomers are compounds which contain polymerizable carbon-to-carbon double bonds and may include acrylates such as acrylic acid, ethyl acrylate, acrylonitrile, etc.; vinyls such as styrenes, vinyl acetate, etc; maleates such as maleic acid, maleic anhydride, maleate esters, etc.

The preferred hydrohalogen-containing polymer may be polyvinyl chloride.

The polymer may be treated in practice of this invention in the form of bodies, sheets, rods, etc., of polymer. It may also be possible to treat surface layers of polymer on other basis materials, e.g., a body of methyl methacrylate bearing a surface layer of polyvinyl chloride, etc.

Thus, according to the invention, a hydrohalogen polymer such as e.g., a polyvinyl chloride, polyvinylidene chloride, polyvinyl dichloride, polychlorostyrene, etc., may be con tucted with an alkali metal alkoxide to give an alkoxide-activutcd surface. The alkali metal alkoxidcs which may be cm pluyctl may be those having the formula MOR wherein M is an x l c l alkali metal and R is an alkyl group. M may be potassium, sodium, lithium, and preferably sodium. R may be methyl, ethyl, npropyl, i-propyl, n-butyl, i-butyl, s-butyl, n-amyl, nhexyl, i-hexyl, n-heptyl, n-octyl, 2-ethyl liexyl, nonyls, decyls, dodecyls, etc. In the preferred embodiment R may be an alkyl group having one to 12 carbon atoms and most preferably one to eight carbon atoms.

Typical illustrative alkoxides MOR which may be employed may include:

lithium methoxide lithium ethoxide lithium n-propoxide lithium i-propoxide lithium 2-ethyl hexoxide sodium methoxide sodium ethoxide sodium n-propoxide sodium i-propoxide sodium n-butoxide sodium 2'ethyl hexoxide sodium dodecoxide potassium methoxide potassium ethoxide potassium n-propoxide potassium i--propoxide The preferred alkoxide may include the ethoxides and propoxides and preferably sodium ethoxide and sodium ipropoxide.

The alkoxides may be dissolved in alcohol ROH and preferably the corresponding alcohol. Preferably sodium ethoxide may be made by adding sodium: metal to an excess of absolute ethanol and the resulting solution used as preparedcontaining an excess of ethanol in which the solid sodium ethoxide is very soluble.

Contact between the hydrohalogen polymer surface and the alkoxide may be effected preferably by dipping the polymer surface into a body of the alkoxide in solution. Temperature during contact may be 2l06 C., preferably 5588 C,, more preferably 60-77 C. Contact time may be 3-5 minutes to 70-8O hours, preferably 5-300 minutes, most preferably 1045 minutes. The temperature and times may be varied. lllustrative temperatures and times may be as set forth in table I.

Temperatures up to the boiling point of the solution may be used.

During contact between the surface and the alkoxide, the surface may become activated. In some cases there may be no apparent visual change in the surface although in other cases, the surface may visually appear slightly modified. The surface may be referred to as an alkoxide-activated surface.

it is a particular feature of this invention that the novel product so prepared may comprise a basis material bearing a hydrohalogen surface including at least one-CH-CX group, wherein X is a halogen, at least a portion of which has been alkoxide activated. This novel product may be characterized by the presence on the polymer surface of double bonds formed by the splitting out of hydrohalogen acid HX to form a polymer surface including at least oneC=C-group.

This novel product may be particularly characterized by its chemical reactivity, and particularly by its ready ability to be oxidized, to accept donor atoms from other molecules, etc.

The alkoxide-activated surface of the hydrohalogen polymer material may be contacted with an oxidizing agent of sufficient strength to convert an olefinic double bond to the corresponding aldehyde, ketone, or carboxyl group. Typical oxidizing agents may include oxygen, potassium permanganate (in aqueous solution) KMnO chromic acid (in aqueous solution), organic peracids (such as perbenzoic acid, peracetic acid, etc.), inorganic peroxides (such as hydrogen peroxide), etc. Oxidation may be carried out at temperatures from ambient room temperature (typically l5-20 C.) to the melting point of the plastic. Preferably, temperatures of from about 55-77 C. are employed. The alkoxide-activated surface is generally contacted with the oxidizing agent at temperatures of from about 66-77 C., for times 2-3 seconds to 2-3 hours. Longer contact times may be employed if desired on certain hydrohalogen polymers [e.g., poly(vinylidene chloride)], but it is preferable to use contact times of only a few minutes, especially with hydrohalogen resins such as polyvinyl chloride.

It is a particular feature of this invention that the product so-prepared may comprise a basis material bearing a hydrohalogen surface including at least one Cl-lCX- group, wherein X halogen, at least a portion of which has been alkoxide activated and the oxygen activated e.g., oxidized. This novel product may be characterized by the presence on the polymer surface of polar (i.e., more strongly polar than before) groups including hydroxyl, aldehyde, ketone, earboxyl, etc.

This novel product may be particularly characterized by its chemical reactivity, and particularly by its ready ability to receive a chemically deposited plate metal.

The oxygen-activated polymer surface (obtained by contact with alkali metal alkoxide and subsequent treatment with an oxidizing agent) may be electrolessly plated as by chemical plating. Electroless plating includes maintaining the surface in contact with a medium containing in solution the metal to be electrolessly plated and a reducing agent capable of reducing the metal to be plated to its zero-valent form. Metals which may be chemically or electrolessly deposited on the activated plastic substrate include e.g., nickel, silver, cobalt, copper, gold, etc. Preferably, metallic nickel is deposited by chemical reduction on the oxygen-activated polymer surface. In a typical nickel deposition, the oxygen-activated polymer surface may be rinsed with water, contacted with aqueous solution of stannous chloride (prepared by combining 50 g./l. of SnCl '2H and 100 g./l. of concentrated hydrochloric acid) at 20 C. for about 1 minute. The polymer may then be rinsed with water and contacted for one minute with aqueous palladium dichloride PdCl (0.2 g./l. of PdCl and containing 5 g./l. of concentrated hydrochloric acid). The polymer surface may again be rinsed with water and then immersed for about 5-l0 minutes (depending upon the thickness of nickel plate desired) in a chemical plating bath (pH approximately 4.5, temperature about 72 C.) containing 50 g./l. of NiCl -6H O, l0 g./l. of NaH PO -H O, and g./l. of Na C H O -2H O. The nickel-plated polymer surface may be removed from the bath and rinsed.

The plated polymer surface may be subsequently electroplated (e.g., with copper, nickel, chromium, etc.) or may be used directly without further plating.

The following exampled (wherein all parts are by weight unless otherwise noted) are submitted for the purpose of illustration only and are not to be construed as limiting the scope of the invention in any way.

EXAMPLE 1 A clean polyvinyl chloride polymer (PVC) panel (10 cm. l0 cm. 3 mm.) may be immersed for minutes at 66 C. in 785 parts of isopropyl alcohol containing 35 parts of sodium isopropoxide (prepared by dissolving 10 parts of sodium in 785 parts of isopropyl alcohol). The alkoxide-activated polyvinyl chloride surface may be removed, rinsed in cold running water for a few seconds, and then placed in l,000 parts of a chromic acid-sulfuric acid solution containing g./l. of CrO and 500 g./l. of H 50, at about 66 C. for approximately 20 minutes. The surface of the polymer may become wetted after being in the oxidizing bath for only about 30 seconds (indicating that the surface had been oxygen activated upon contact). The polymer may be removed, rinsed, immersed in stannous chloride solution (50 g./l. of SnCl -2H 0 and 100 g./l. of concentrated HCl for 1 minute, at room temperature, removed, rinsed in H O, immersed in palladium dichloride PdCl solution (0.2 g./l. of PdCl and 5 g./l. of concentrated hydrochloric acid) at room temperature, removed and placed in a chemical nickel plating bath at 71 C. (containing 50 g./l. of NiCl 'GH O, l0 g./l. of sodium citrate 21-1 0, and 10 g./l. of NaH PO -H O) for about 5 minutes. The nickelplated polymer may be removed, rinsed, and a 0.003 cm. thickness of dull copper electrolytically deposited on the nickel-plated surface. The polymer may then be removed from the bath and plated with an additional 0.0075 mm. of bright nickel.

The plated panel may be subjected to a standard thermocycle rest which comprises heating the plated polymer for 60-70 minutes'at 96 C., then at room temperature (27-32 C.) for about 10 minutes, and then cooling to about l0 C. for 60-70 minutes. This cycle, when repeated three times for each plated article, may be termed a standard thermocycle test. No blistering, peeling, or lifting of the metal from the panel was observed after completion of the standard thermocycle test.

EXAMPLES 2-21 Table ll summarizes the results obtained using the general procedure of example 1, but with different alkali metal alkoxides and various hydrohalogen polymers.

The following abbreviations are employed in table ll:

PVC=Polyvinylchloride PVDC=Polyvinyldichloride S=Polyvinylidenechloride The results of the standard thermocycle test were used to measure adhesion quality and are rated as follows:

Good-No blistering or peeling of metal.

Fair-Some blistering or peeling, but no complete separation of metal.

PoorMetal coating completely separated from the surface of the plastic over the entire panel.

TABLE II Summary of Adhesion Results Obtained from Various Alkali Metal Alkoxides Ex. Alkali metal No. Plastic alkoxide Solvent Adhesion 2 PVC None None (control) Poor 3 PVC None 1 n-C.H OH Poor 4 PVC n C H ONa n-C,H 0H Fair 5 PVC None !-C,H OH Poor 6 PVC t-C,H,OK K-CJl OH Fair 7 PVC None CH,OH Poor 8 PVC CH,ONa CH OH Fair 9 PVC None iso-C,H,OH Poor 10 PVC iso-C,H,OK is0-C H OH Good I 1 PVC iso'C,H,ONa iso-C,H OH Good 12 PVC None C,H,OH Poor 13 PVC CJISONa C H OH Fair l4 PVDC None CzHioH Poor l5 PVDC CH50Na C,H5OH Good l6 PVDC None isD-C H OH Fair l7 PVDC iso-C,H ONa iSO-C H ,OH Good l8 5 C,H,ONa C,H,OH Poor 1) S C,H,0na C,H,OH Good 20 5 None iso-C,,H 0H Poor 2i 5 iSO-C l-LOK is0'C,H OH Good sesame Control examples No oxidizing agent was used.

No oxidizing agent was used: electrcless Ni coating peeled away.

It will be apparent to those skilled in the art that control examples 2, 3, 5, '7, 9, 12, 14 and 20 did not yield satisfactory results. On the other hand, examples 4, 6, 8, l0, 1 1, l3, l5, 17, 18, 19 and 21 permitted attainment of satisfactory results. By comparison, for example, of examples 9 and 10, it will be apparent that practice of this invention may permit attainment of outstanding results where no satisfactory results may other wise be attained by other techniques. Further improvements may be shown by comparing examples l6 and i7.

EXAMPLES '2.22'7

In the following examples, isopropyl alcohol was employed as the solvent. The force required to separate metal from the polymer surface was determined as follows: Each plated polymer panel (10 crn. l cm. 3 mm.) was cut in order to obtain a portion about 2.5 cm. wide and 8--9 cm. long. The metal coating was peeled back at one end by hand until a sufficient grip on the metal could be obtained. The panel was mounted on a fixed holder and fastened to a rod with a clamp. The clamp was connected to a strain gage. A force was applied and the plate was slowly pulled from the polymer surface at a rate of 1.8 cmjminute. The separation force required to pull the metal away from the polymer surface at this uniform rate was determined from the strain gage. Separation force was expressed in kilograms per centimeter of width and the maximum value was recorded. To give a comparison with results obtained by the thermocycle test, values of about 0.13 to 0.27 are fair, values above 0.27 are good, and values below 0.13 are poor.

The results are summarized in table ill.

TABLE Ill Adhesion (as Separation Ex. Alkali metal measured hy force No. Polymer dlkoxide lhermocycle) (kg/cm.)

22 PVC None (control) Poor 23 PVC i-C l'LONa Good 032 24 PVDC None (control) Fair 0. I 8 25 PVDC i-C H-,0Na Good 036 26 5 None (control) Poor 27 S i-C hLoNa Good 0.71

From table ill it can be readily seen that the polymers of examples 23, 25, and 27 had significantly better adhesion pro parties after treatment with alkali metal alkoxide when compared with the polymers of corresponding examples 22, 24, and 26 which were not alkoxide activated. In examples 22 and 26 the nickel plate separated completely duringthe thermocycle test.

Although this invention has been described by reference to preferred illustrative examples, it will be apparent to those skilled in the art that various modifications and changes may be made thereto which fall within the scope of this invention.

We claim:

1. The method of modifying a hydrohalogen polymer surface which comprises contacting the [hydrohalogen polymer surface with an alkali metal alkoxide MOR wherein M is an alkali metal and R is an alkyl group having one to l2 carbon atoms thereby forming an alkoxide-activated surface with chromic acid thereby forming an oxygen-activated alkoxideactivated surface.

2.. The method of modifying a hydrohalogen polymer sur face which corn rises contacting the h drohalogen olymer surrace with an a kali metal alkoxide M R wherein IS an alkali metal and R is an alkyl group having one to 12 carbon atoms thereby forming an alkoxide-activated surface, and contacting acid alkoxide-activated surface with potassium permanganate thereby forming an oxygen-activated alkoxideactivated surface. 

2. The method of modifying a hydrohalogen polymer surface which comprises contacting the hydrohalogen polymer surface with an alkali metal alkoxide MOR wherein M is an alkali metal and R is an alkyl group having one to 12 carbon atoms thereby forming an alkoxide-activated surface, and contacting acid alkoxide-activated surface with potassium permanganate thereby forming an oxygen-activated alkoxide-activated surface. 